This invention relates to the production of aluminum chloride. More particularly, this invention relates to the production of aluminum chloride from raw materials containing aluminum compounds and silicon compounds either physically or chemically combined.
The production of aluminum chloride for use as a Friedel-Crafts catalyst or as a feed material for the production of metallic aluminum conventionally has involved a first refinement of raw ore to recover a substantially pure aluminum oxide (Al.sub.2 O.sub.3) which is then chlorinated to produce aluminum chloride. While there has been exploration of the possible chlorination of raw ores containing other impurities, this has usually been considered to be economically inferior because of the wasteful chlorination of the impurities such as silicon or the like. Furthermore, the presence of such impurities sometimes interferes with the chlorination of the aluminum compounds thus lowering the recoverable yield of the aluminum chloride from the raw material via direct chlorination.
It would therefore be valuable to have a process wherein the aluminum values in a raw material such as clay could be recovered in an economically useful percentage while at the same time inhibiting the chlorination of impurities, thus lowering the overall usage of chlorine as well as lowering the need for recycling of the impurities to recover chlorine values therefrom.
Previously it has been proposed that alumina or clay should have controlled porosity or particle size to obtain better chlorination of the Al.sub.2 O.sub.3 values. For example, Staib U.S. Pat. No. 1,878,013 and German Patentschrift 531,400 teach the addition to an oxide (such as aluminum oxide) of voluminous carbonaceous matter such as peat or sawdust or the like as a reducing agent followed by drying and carbonizing to form an extremely porous body having a maximum surface of attack offered to chlorine gas. Similarly, Hille et al discuss the effect of particle size and distribution, surface area and pore size on chlorination of alumina in an article entitled "The Production of Anhydrous Aluminum Chloride from .gamma.-Alumina in a Fluidized Bed" on pp. 850-855 of Angew Chem. 72 (1960).
While the foregoing publications discuss chlorination of oxides without necessarily addressing themselves to the presence of impurities, the chlorination of clay and the effect of the presence of SiO.sub.2 therein as well as the effect of the presence of SiCl.sub.4 on the chlorination of mixtures of Al.sub.2 O.sub.3 and SiO.sub.2 such as found in clays are discussed in Staib U.S. Pat. No. 1,866,731; British Patent Specification 305,578; and in an article by D. J. Milne entitled "Chlorination of Bauxite in the Presence of Silicon Tetrachloride" published in Metallurgical Transactions on pp. 486-488 of Volume 6B (September 1975). See also Spitzin et al "Obtaining Anhydrous Aluminum Chloride from Natural Aluminum-Containing Materials" Z. Anorg. und Allgmeine Chem. 196 pp. 289-311 (1931). Each of these publications notes that the presence of SiCl.sub.4 suppresses chlorination of SiO.sub.2.
There also have been investigations as to the effect of heat on the chlorination reaction particularly with regard to exothermic heat balances. See Brode et al U.S. Pat. No. 1,982,194; Wurster "Commercial Production of Anhydrous Aluminum Chloride" Z. fur Angewandte Chemie, Vol. 43, pp. 877-880 (1930); and French Pat. No. 645,335. The latter patent also commends the use of CO and Cl.sub.2 over phosgene so as to generate more heat.
There seems to be little appreciation however in the above publications that maintaining the chlorination rate at a lower temperature has any effect on the selective chlorination of alumina or silica. In fact, Voronin et al in "Production of Anhydrous Aluminum Chloride from ChasovYar Clay" Zh Khim Prom 7, pp. 143-149 (1930) noted that beginning at 550.degree. only part of the chlorine was used to chlorinate Al.sub.2 O.sub.3 with the remainder used on the chlorination of SiO.sub.2 and then Fe.sub.2 O.sub.3 and TiO.sub.2. They stated that the percentage of the total chlorine used for the chlorination of Al.sub.2 O.sub.3 was independent of temperature beginning at 550.degree. and going up to 850.degree.. They compared their results to a previous report by Seward and Kugelhen (U.S. Pat. No. 1,147,836).
Finally, there have been favorable comments on the use of gaseous reducing agents. The Voronin et al article, referred to above, favorably reports on the use of air with solid carbon and Cl.sub.2 to produce CO or phosgene which, they postulate, are better reducing agents. French Pat. No. 645,335 prefers CO over phosgene -- but this again is related to a desire for sufficient production of heat to maintain a heat balance in the overall chlorination reaction.